How do I describe a collection in Mongo?

So this is Day 3 of learning Mongo Db. I'm coming from the MySql universe...

A lot of times when I need to write a query for a MySql table I'm unfamiliar with, I would use the "desc" command - basically telling me what fields I should include in my query.

How would I do that for a Mongo db? I know, I know...I'm searching for a schema in a schema-less database. =) But how else would users know what fields to use in their queries?

Am I going at this the wrong way? Obviously I'm trying to use a MySql way of doing things in a Mongo db. What's the Mongo way?

Type the below query in editor / mongoshell

var col_list= db.emp.findOne();
for (var col in col_list) { print (col) ; }

output will give you name of columns in collection :

_id
name
salary

There is no good answer here. Because there is no schema, you can't 'describe' the collection. In many (most?) MongoDb applications, however, the schema is defined by the structure of the object hierarchy used in the writing application (java or c# or whatever), so you may be able to reflect over the object library to get that information. Otherwise there is a bit of trial and error.

This is my day 30 or something like that of playing around with MongoDB. Unfortunately, we have switched back to MySQL after working with MongoDB because of my company's current infrastructure issues. But having implemented the same model on both MongoDB and MySQL, I can clearly see the difference now.

Of course, there is a schema involved when dealing with schema-less databases like MongoDB, but the schema is dictated by the application, not the database. The database will shove in whatever it is given. As long as you know that admins are not secretly logging into Mongo and making changes, and all access to the database is controller through some wrapper, the only place you should look at for the schema is your model classes. For instance, in our Rails application, these are two of the models we have in Mongo,

class Consumer
    include MongoMapper::Document

    key :name, String
    key :phone_number, String
    one :address
end

class Address
    include MongoMapper::EmbeddedDocument

    key :street, String
    key :city, String
    key :state, String
    key :zip, String
    key :state, String
    key :country, String
end

Now after switching to MySQL, our classes look like this,

class Consumer < ActiveRecord::Base
    has_one :address
end

class Address < ActiveRecord::Base
    belongs_to :consumer
end

Don't get fooled by the brevity of the classes. In the latter version with MySQL, the fields are being pulled from the database directly. In the former example, the fields are right there in front of our eyes.

With MongoDB, if we had to change a particular model, we simply add, remove, or modify the fields in the class itself and it works right off the bat. We don't have to worry about keeping the database tables/columns in-sync with the class structure. So if you're looking for the schema in MongoDB, look towards your application for answers and not the database.

Essentially I am saying the exactly same thing as @Chris Shain :)

How do I describe a collection in Mongo?

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